1. Field of the Invention
The present invention relates to a photosensitive composition preferably used in super-microlithography processes such as the manufacture of super LSI and high capacity microchips, and other photo-publication processes. More specifically, the invention relates to a positive photoresist capable of forming a highly refined pattern with electron beams, X-rays or EUV rays, and a resist composition suitable for fine processing of semiconductor devices using electron beams, X-rays or EUV rays (wavelength: 13 nm or so).
2. Description of the Related Art
In the manufacturing process of semiconductor devices such as IC and LSI, fine processing by lithography using photoresist compositions has been conventionally carried out. In recent years, with the increment of integration of integrated circuits, ultrafine pattern formation of the levels of a sub-micron and quarter-micron has come to be required. Under such a circumstance, the exposure wavelengths show a tendency to be shortening, such as from g-ray to i-ray, further to KrF excimer laser beam. Further, lithography using electron beams, X-rays or EUV rays in addition to excimer laser beams has been developed nowadays.
In particular, electron beam lithography is taken as the pattern forming technique of the next generation or the next of the next generation, so that resists of high sensitivity and high resolution are required. The increase in sensitivity is very important object in view of shortening of the processing time of wafers, but in positive resists for electron beams, pursuit of increment of sensitivity is accompanied by not only reduction of resolution but also deterioration of line edge roughness, so that the development of a resist satisfying these characteristics at the same time is strongly desired. Here, line edge roughness means that the edge of the interface between the line pattern of a resist and a substrate irregularly changes in perpendicular direction to the line direction attributable to the characteristics of the resist, and the edge looks unevenly when it is observed from right above. This unevenness is transferred to the substrate by etching processing with the resist as a mask and deteriorates electric characteristic and results in the reduction of yield. In particular, line edge roughness is an extremely important object to be solved in a hyperfine region of 0.25 μm or less. High sensitivity, high resolution, a good pattern form and good line edge roughness are in relationship of trade-off, and how to satisfy these factors at the same time is a very important object.
Further, when EUV is used as the light source, since wavelengths of the lights belong to the extreme ultraviolet region having high energy, there is a problem of contrast reduction due to concentration of photochemical reaction such as the tendency to be negative attributable to EUV rays and the like. In lithography using X-rays or EUV rays, it is also an important object to reconcile high sensitivity and high resolution, and the resolution of this problem is indispensable.
As the resist suitable for lithographic process using electron beams, X-rays or EUV rays, chemical amplification resists utilizing acid catalytic reaction are mainly used from the viewpoint of the enhancement of sensitivity, and in positive resists, phenolic polymers having properties that are insoluble or hardly soluble in an alkali developing solution but become soluble in an alkali developing solution by the action of an acid (hereinafter referred to as phenolic acid-decomposable resin), and chemical amplification resist compositions comprising acid generators are effectively used as the main components.
In connection with these positive resists for electron beams, X-rays or EUV rays, some resist compositions containing phenolic acid-decomposable resin are known (e.g., JP-A-2002-323768 (The term “JP-A” as used herein refers to an “unexamined published Japanese patent application”.), JP-A-6-41221, Japanese Patent No. 3173368, JP-A-2000-122291, JP-A-2001-114825, and JP-A-2001-206917).
Further, when light sources such as electron beams, X-rays and EUV are used, exposure is carried out under a vacuum, so that compounds having a low boiling point such as solvents and resist materials decomposed by high energy are volatilized to thereby contaminate the exposure apparatus, i.e., outgassing is a serious problem. In recent years, various investigations are in progress on the reduction of outgassing, and a variety of trials are suggested, e.g., restraint of volatilization of low molecular weight compounds by forming a top coat layer (e.g., refer to EP 1480078), and addition of a radical trapping agent capable of inhibiting decomposition of a polymer (e.g., refer to U.S. Pat. No. 6,680,157). Some contrivances of outgassing are also required in connection with acid generators.
In addition, contrivances such as linking of a benzene ring of triphenyl sulfonium (JP-A-2003-149800), and addition of a base capable of decomposing and becoming a neutral compound by actinic radiation exposure (Japanese Patent No. 3549592) have been tried.
However, it is the present situation that high sensitivity, high resolution, good line edge roughness and low outgassing in a hyperfine region cannot be satisfied at the same time with any of these combinations.